While he's not directly in the Harry Potter books, his legacy and impact are felt through mentions and references:
* Albus Dumbledore's past: We learn that Dumbledore and Grindelwald were close friends who shared a vision of a world ruled by wizards, but their views diverged, leading to a duel that ended with Dumbledore defeating Grindelwald.
* The Elder Wand: Grindelwald's quest for the Elder Wand is a significant plot point in both the Fantastic Beasts series and the Harry Potter series, as it ultimately leads to its possession by Harry Potter.
As for Grindelwald's characterization: He is a complex and highly ambitious dark wizard who believes in wizarding supremacy and aims to rule the world. He possesses incredible magical abilities and a charisma that allows him to attract followers and gain power.
Therefore, while not in the Harry Potter books directly, Grindelwald is a central figure in the wizarding world's history and is definitively a dark wizard.